1. Field of the Invention
The present invention relates to a method and apparatus for removing oxidizable contaminants in water to achieve high purity water for industrial use. The present invention is used in conjunction with conventional purification systems which remove certain inorganic and non-oxidizable contaminants. Some of the impurities can be removed through conventional filters. However, many organic impurities and other inorganic solids are not removed by conventional filtering means. The present invention provides a system whereby the impurities, and in particular organic carbon and other organic impurities are significantly reduced in electronic quality water.
2. Description of the Prior Art
One key element of the present invention purification process involves the concept of reducing the oxygen demand in the water stream. Since the contaminants which are not removed by conventional filtering systems are usually oxidizable materials, the oxidation of such materials serves to degrade and eliminate them. This concept is described in general terms in the paper "Innovative Oxidation Technology for Waste Pretreatment", by Stanley A. Peterson and Nicholas S. Zaleiko, which was published in the Feb. 1981 issue of Water/Engineering & Management ("Oxidation Article"). The method described in the Oxidation Article is an improvement over a previously known "wet oxidation process" which is used to treat municipal and industrial aqueous effluents containing oxidizable organic compounds. The wet oxidation process comprises forcing compressed air through the heated effluents (heated to temperatures of 150 degrees centigrade to 320 degrees centigrade) under pressure (300 to 3000 psig) in the presence of cupric ion as an oxidation catalyst. Under conditions of the process, organic compounds present in the effluent are degraded by sequential oxidation to carbon dioxide, water and refractory organic compounds such as formic and acetic acids. Additional treatments are required to remove the refractory organic compounds. As discussed in the Oxidation Article, the process described therein includes subjecting the liquid to be purified to cavitation, adding a free radical initiator, inducing supplementary cavitation and exposing the liquid to ultraviolet (UV) light. When cavitation is applied, the bubble explosion in cavitation ruptures the thin cell membrane of organic sludges. In addition to oxidation by the free radical, the exposure to ultraviolet light provided for additional free radical oxidation.
The process discussed in the Oxidation Article was further described in a patent application filed by Nicholas Zaleiko entitled Method And Apparatus For Oxidative Degradation Of Water Contaminants. That application was subsequently abandoned.
The above referenced application and the Oxidation Article concentrated on removing impurities from waste waters and specifically concerned the following:
(1) Oxidation of process chemicals such as dyes, fatty acids, sludges and certain organics;
(2) Sanitary and industrial wastewater treatment at remote locations;
(3) Specific industrial wastes such as cyanides, sulfites, phenols, fat renderings, food processing pigments, pharmaceutical, soft drink and alcohol-type wastes;
(4) Pulp and paper bleaching and processing;
(5) Semicatalytic oxidation of refractory compounds such as those from plating and photographic wastes;
(6) Treatment of various in-plant side streams such as digester supernatant and thickener overflows;
(7) Destruction and treatment of septic wastes.
This prior art process concentrated on the above applications and did not expand the treatment process to other applications such as purifying water prior to its use in industrial applications such as cleaning semiconductor wafers. In addition, inventor Zaleiko included several complicated steps such as heating the liquid. The present invention greatly simplifies the process and utilizes it in new and non-obvious applications.
The inventor is also aware of the following prior art patents which relate to various purification and treatment processes:
1. U.S. Pat. No. 2,722,498 issued to Morrell et al. in 1955 for "Process For Separating Organic Material From Inorganic Material".
2. U.S. Pat. No. 3,288,295 issued to Kelly in 1966 for "Tank Cover Structures".
3. U.S. Pat. No. 3,401,115 issued to Meyer et al. in 1968 for "Sewage Treatment System".
4. U.S. Pat. No. 3,480,543 issued to Hildebrand in 1969 for "Process And Apparatus For Disinfection Of Sewage".
5. U.S. Pat. No. 3,672,823 issued to Boucher in 1972 for "Method Of Sterilizing Liquids".
6. U.S. Pat. No. 3,677,409 issued to Ferm et al. in 1972 for "Sewage Treatment System".
7. U.S. Pat. No. 4,013,552 issued to Kreuter in 1977 for "Sewage Treatment Process".
8. U.S. Pat. No. 4,076,617 issued to Bybel et al. in 1978 for "Sonic Cavitation And Ozonation Of Waste Material".
9. U.S. Pat. No. 4,144,152 issued to Kitchens in 1979 for "Dehalogenation Of Halogenated Compounds".
The processes described in the above patents differ from the Oxidation Article and the abandoned Zaleiko patent application, and also differ from the specific application to purifying waters before they are used in industrial applications, etc.
The inventor is also aware of the following patents which disclose various apparatus and/or methods by which cavitation and other shock treatments are employed in a cleaning process:
1. U.S. Pat. No. 2,660,564 issued to Davis in 1953 for "Method Of Reducing The Density of Aerogels And Similar Materials".
2. U.S. Pat. No. 2,832,545 issued to Segraves for "Supersonic Jet Grinding Means And Method".
3. U.S. Pat. No. 2,911,787 issued to Barry in 1959 for "Inlet Probe".
4. U.S. Pat. No. 3,265,090 issued to Elliott in 1966 for "Fluid Flow Controller".
5. U.S. Pat. No. 3,278,165 issued to Gaffney in 1966 for "Method And Apparatus For Generating Acoustic Vibrations In Flowing Fluids".
6. U.S. Pat. No. 3,504,945 issued to Leibundgut et al. in 1970 for "Pneumatic Conveyer System".
7. U.S. Pat. No. 3,538,803 issued to Joseph in 1970 for "Cavitation Machining Apparatus".
8. U.S. Pat. No. 3,674,216 issued to Blair in 1972 for "Treating Liquid Waste Effluent".
9. U.S. Pat. No. 4,053,110 issued to Schalkowsky et al. in 1977 for "Shock Press".
10. U.S. Pat. No. 4,284,245 issued to Fishgal in 1981 for "Machine Lubrication System".
11. U.S. Pat. No. 4,506,834 issued to Ek in 1985 for "Method And Device For Dispersing Material".
While there are many prior art references dealing with the inducement of cavitation and other shock effects utilized in purification processes to treat wastes, none of the references disclose the concept of the present invention treatment process employed prior to utilization of the water in industrial cleaning or consumption.
Much work has been done on microbial control and treatment systems employing chemicals to destroy the microorganism present in recirculating water. These systems, commonly used in large water re-circulation systems, are chemical treatment processes involving oxidation of the organic material. They have a high cost and maintenance as well as presenting some hazard to the operators.
A need has developed for a compact and reliable treatment system employing free-radical chemical reaction capabilities of auto-oxidation of both organic and inorganic materials present in water enhanced by the addition of catalysts so that the reactions can be induced to rapid completion by high energy transfer. Prior art of aerobic or chemical treatment systems have not satisfied the need.
There exists a significant need to clean the recirculating water system of cleansing waters used for various industrial applications such as the cleaning of silicon wafers, so as to assure that certain oxidizable contaminants are removed from the water before it is used in the cleaning operation.